The present invention relates to a steering shaft locking device for disabling steering by engaging a locking bar with the steering shaft.
In recent years, electronic steering shaft locking devices for automobiles have been proposed. An electronic steering shaft locking device disables steering by engaging a locking bar with a steering shaft using the drive force of an actuator, such as a motor or the like. Japanese Laid-Open Patent Publication Nos. 2003-063354 and 2000-095066 describe examples of such steering shaft locking devices.
An example of this type of steering shaft locking device is shown in FIG. 1. An electronic steering shaft locking device 100 disables steering by engaging a locking bar 130 with a steering shaft 120 using the rotation drive force of a motor 110.
In an automobile provided with this type of steering shaft locking device 100, the locking bar 130 is engaged with the steering shaft 120 to lock the steering shaft 120 (locked state) before the engine starts. In the locked state, steering is disabled. For example, when a driver performs an operation to start the engine, a steering shaft lock ECU 140 drives the motor 110 (for example, forward rotation). Then, the locking bar 130 separates from the steering shaft 120 such that the steering shaft 120 is unlocked (unlocked state). In the unlocked state, steering is enabled. When the locking bar 130 is moved from a lock position to an unlock position, an unlocked state sensor switch 150 is activated. The steering shaft lock ECU 140 recognizes that the steering shaft 120 is unlocked based on the ON state of the unlocked state sensor switch 150 and stops the forward rotation of the motor 110. Unlocking of the steering shaft 120 is one condition required for starting the engine.
The steering shaft 120 is unlocked immediately after the engine stops. For example, when the driver opens the door to exit the vehicle and then closes the door, the steering shaft lock ECU 140 drives the motor 110 (for example, reverse rotation). Thus, the locking bar 130 engages the steering shaft 120 and locks the steering shaft 120. When the locking bar 130 is moved from the unlock position to the lock position, a locked state sensor switch 160 is activated. The steering shaft lock ECU 140 recognizes that the steering shaft 120 is locked based on the ON state of the locked state sensor switch 160 and stops the reverse rotation of the motor 110.
From the perspective of locking an object, automobiles are provided with door locking devices similar to steering shaft locking devices. For example, Japanese Laid-Open Utility Model Publication No. 06-049672 discloses a door locking device which reduces the noise that is generated when actuated.
As mentioned above, the steering shaft locking device 100 moves the locking bar 130 when switching from a locked state to an unlocked state (unlocking operation) or when switching from an unlocked state to a locked state (locking operation). During the unlocking operation, the locking bar 130 that is engaged with the steering shaft 120 must be pulled out of the steering shaft 120 by the steering shaft locking device 100. During the locking operation, however, the steering shaft locking device 100 may move the locking bar 130 into the steering shaft 120 with a relatively small force. That is, a larger force is required when moving the locking bar 130 during the unlocking operation than when moving the locking bar 130 during the locking operation.
Furthermore, the unlocking of the steering shaft 120 is one of the conditions necessary for starting the engine. Therefore, it is desirable that the time required for the unlocking operation be shorter than the time required for the locking operation to reduce the time between the initiation of the engine starting operation and the completion of engine starting.